JP7311182B1 - Precious metal recovery agent and method for recovering precious metal - Google Patents

Abstract

A novel precious metal recovery agent and recovery method are provided. A precious metal recovery agent containing coffee cherries as an active ingredient is used to recover precious metals from a metal solution in which precious metals are dissolved. Additionally, the coffee beans are selected from the group consisting of ground rind, roasted coffee beans, roasted and ground coffee beans, and roasted and ground coffee bean residue. Further, the metal solution is a solution in which noble metals, iodine, salts of iodine, and reducing agents are dissolved. [Selection figure] None

Description

TECHNICAL FIELD The present invention relates to a noble metal recovery agent and a noble metal recovery method.

Precious metals such as gold and palladium are essential for the manufacture of various electronic products, automobile catalysts and the like. While the production of electronic products, autocatalysts, etc. continues to increase, these precious metals are limited in their output. In order to continue the stable production of electronic products, automobile catalysts, etc., it is important to recover precious metals from metal waste liquids and the like obtained from discarded products and to recycle them.

As a method for recovering precious metals, for example, a chemical recovery method using a solvent extraction method, an ion exchange method, or the like is known. However, with these methods, it is difficult to economically recover precious metals contained in metal waste liquids at low concentrations (for example, 10 ppm or less). Therefore, in recent years, the development of a method capable of recovering even a low-concentration noble metal has been advanced. For example, in Patent Document 1, a dried product of red algae of the cyanidial order, a dried product of a red algae of the cyanidial order, a dried product of a red algal cell-derived product of the cyanidial order, or an artificial product that imitates the dried product of the cell or the dried product of the cell-derived product A metal recovery agent or metal compound recovery agent is disclosed, comprising:

In addition, individuals and groups of poor people in developing countries mine gold (small-scale mining). In small-scale gold mining, for example, after adding mercury to pulverized gold ore to obtain gold amalgam, the gold amalgam is heated to evaporate the mercury, and the remaining crude gold is obtained. (For example, Non-Patent Document 1).

WO2018/155687

UNEP, 2013, Global Mercury Assessment 2013: Sources, Emissions, Releases and Environmental Transport. , UNEP Chemicals Branch, Geneva, Switzerland

As described above, there are several known methods capable of recovering even low-concentration noble metals and noble metal recovering agents used in these methods. On the other hand, due to the increase in options for precious metal recovery agents and precious metal recovery methods themselves, consideration should be given not only to the recovery efficiency of precious metals, but also to the cost and ease of procurement of raw materials, manufacture of precious metal recovery agents, implementation of precious metal recovery methods, etc. can be selected.

In addition, small-scale gold mining using mercury poses problems such as adverse effects on workers' health and environmental pollution due to mercury released into the environment. A cheap and safe alternative to mercury-based small-scale mining of gold is needed.

Accordingly, an object of the present invention is to provide a novel noble metal recovery agent and a noble metal recovery method.

The present inventors have found that coffee beans and silver skin (roasted and ground coffee beans, residue after extraction of extract from the coffee beans, etc.) selectively adsorb precious metals. The present invention is based on this new finding.

TECHNICAL FIELD The present invention relates to a noble metal recovery agent containing coffee cherries as an active ingredient.

The active ingredient of the noble metal recovery agent may be coffee beans or silver bark.

The coffee beans, which are the active ingredient, may be at least one selected from the group consisting of ground husks, roasted coffee beans, roasted and ground coffee beans, and roasted and ground coffee bean residues.

The above-described invention relating to the precious metal recovery agent can also be regarded as a use (application) for recovering precious metals from coffee cherries.

The present invention also relates to a method for recovering precious metals, comprising a step of recovering precious metals from a metal solution in which precious metals are dissolved, using the precious metal recovery agent according to the present invention. The method for recovering precious metals according to the present invention can selectively recover precious metals with high efficiency by using the above-described noble metal recovery agent according to the present invention.

In the recovery method described above, the noble metal may include gold or palladium.

In the recovery method described above, the metal solution may also be a solution in which noble metals, iodine, iodine salts, and reducing agents are dissolved. In this recovery method, precious metals can be recovered from a metal solution in which precious metals, iodine, iodine salts, and reducing agents are dissolved, using a precious metal recovery agent containing coffee cherries as an active ingredient, which adversely affects workers and the environment. Safe recovery of precious metals is possible without the need to use materials. Furthermore, since the necessary materials can be procured at low cost, and the recovery rate of the precious metal is high and the cost can be reduced, the precious metal can be recovered at low cost. Therefore, the recovery method having the above configuration can be suitably used for small-scale mining of precious metals (for example, gold).

The iodine salt may be at least one selected from salts of iodine and alkali metals and salts of iodine and alkaline earth metals.

The reducing agent may contain ascorbic acid.

The present invention further provides a kit for recovering precious metals from a metal solution in which noble metals, iodine, salts of iodine, and reducing agents are dissolved, comprising at least a precious metal recovery agent, wherein the noble metal recovery agent is a It also relates to a kit, which is a precious metal recovery agent.

The kit may further contain a reducing agent in addition to the noble metal recovery agent.

According to the present invention, it is possible to provide a novel noble metal recovery agent containing coffee cherries as an active ingredient. According to the present invention, it is also possible to provide a novel noble metal recovery method using the noble metal recovery agent.

DETAILED DESCRIPTION OF THE INVENTION Embodiments for carrying out the present invention will be described in detail below. However, the present invention is not limited to the following embodiments.

[Precious metal recovery agent]
The precious metal recovery agent according to the present embodiment contains coffee cherries as an active ingredient.

Coffee cherry is the fruit of a plant belonging to the Rubiaceae genus Rubiaceae Coffea. Coffee cherries include the outer skin, pulp, parchment, silver skin and coffee beans. The noble metal recovery agent according to this embodiment may contain all or part of coffee cherries as an active ingredient. A portion of the coffee cherry may be at least one selected from the group consisting of the above-described outer skin, pulp, endocarp, silver skin and coffee beans.

Since the noble metal recovery agent according to the present embodiment exhibits the effect of being able to selectively and efficiently recover noble metals more remarkably, it preferably contains silver bark or coffee beans as an active ingredient. It is more preferable to include

Coffee beans can be obtained, for example, by removing the outer skin, pulp, endocarp and silver skin from coffee cherries.

The silver skin can be obtained, for example, by removing the outer skin, pulp and endocarp from coffee cherries, and then separating the silver skin from the coffee beans.

The type of coffee cherries used as an active ingredient is not particularly limited, but from the standpoint of availability, coffee cherries of plant species whose coffee beans are used for drinking can be preferably used. Specific examples include coffee berries such as Coffea arabica L, Coffea robusta Linden, and Coffea liberica.

The coffee cherries used as the active ingredient may be green coffee cherries or processed coffee cherries. Green coffee cherries refer to the coffee cherries themselves or parts thereof (eg, the seeds themselves obtained from the coffee cherries, the silver skins themselves). Processed coffee cherries refer to coffee cherries themselves or a portion of them that have been processed. Processing includes, for example, heat processing, pulverization processing, extract removal processing, and combinations of one or more of these.

Heat processing is carried out by heating green coffee cherries (e.g., green coffee beans, raw silver skin) or processed coffee cherries (e.g., processed coffee beans, processed silver skin). be able to. The heating method is not particularly limited, and for example, dry heating such as roasting, wet heating using a heat medium (eg, water or oil), dielectric heating, or the like can be applied. The temperature during heat processing may be, for example, about 80 to 200.degree. The heat processing time may be, for example, about 5 minutes to 3 hours. The heat processing is preferably roasting, which is commonly used for heat processing green coffee beans. In this specification, the coffee beans that have undergone heat processing are sometimes referred to as "heated coffee beans", and the coffee beans that have undergone roasting processing are particularly referred to as "roasted coffee beans". Roasted coffee beans are sometimes classified into light roast, medium roast, and dark roast according to the degree of roasting, but the precious metal recovery agent according to the present invention recovers precious metals regardless of the degree of roasting. can do.

The pulverization process is carried out by pulverizing green coffee cherries (e.g., green coffee beans, raw silver skin) or processed coffee cherries (e.g., processed coffee beans, processed silver skin). be able to. The pulverization can be carried out using, for example, coffee mills, grinders, and other devices commonly used for pulverizing roasted coffee beans. The degree of pulverization (particle size of coffee cherries after pulverization) is not particularly limited, but the particle size (major axis) of pulverized coffee cherries is usually 1 mm or less. When the active ingredient is coffee beans, the degree of grinding of the coffee beans may be, for example, extra-fine, fine, medium-fine, medium or coarse. In this specification, the pulverized silver skin is called "pulverized silver skin", the pulverized coffee beans are called "pulverized coffee beans", and roasting and pulverizing are performed in this order. The roasted coffee beans are sometimes called "roasted and ground coffee beans".

Extract removal processing involves contacting green coffee cherries (e.g., green coffee beans) or processed coffee cherries (e.g., processed coffee beans) with a solvent or steam, followed by solvent or steam, and solvent or It can be carried out by removing the steam extract to obtain a residue. Examples of solvents include water, lower alcohols (eg, methanol, ethanol), and mixed solvents thereof. Vapors include, for example, vapors of these solvents. The temperature of the solvent or steam is preferably high, for example, 60 to 100° C., because the extract extraction efficiency is high. In the present specification, coffee beans that have been subjected to extract removal processing are referred to as "coffee bean residues", and roasted and ground coffee beans that have been subjected to extract removal processing are particularly referred to as "roasted and ground coffee bean residues". There is

Since the noble metal recovery agent according to the present embodiment has a higher noble metal recovery efficiency, the active ingredient is a group consisting of pulverized silver skin, roasted coffee beans, roasted and pulverized coffee beans, and roasted and pulverized coffee bean residue. It is preferable to use at least one more selected.

In the noble metal recovery agent according to the present embodiment, one kind of coffee cherries may be used alone as an active ingredient, or two or more kinds may be used in combination. The combination as used herein includes combining coffee cherries of a plurality of plant species and combining portions of coffee cherries (for example, combining coffee beans and bark).

The noble metal recovery agent according to the present embodiment may consist of the coffee cherries themselves, which are the active ingredients, or may contain ingredients other than the active ingredients. Components other than the active ingredient include, for example, water, carriers such as lower alcohols (eg, methanol, ethanol), preservatives, antifungal agents, and the like.

The invention relating to the precious metal recovery agent can also be regarded as the invention relating to the use (application) of coffee cherries for recovering the precious metal.

[Precious metal recovery method]
A method for recovering precious metals according to the present invention is characterized by recovering precious metals using the precious metal recovery agent according to the present invention.

A method for recovering precious metals according to one embodiment includes a step (recovery step) of recovering precious metals from a metal solution in which noble metals are dissolved using a noble metal recovery agent. The recovery step includes, for example, a step of adding a noble metal recovery agent to a metal solution containing a noble metal, a step of adsorbing the noble metal to the noble metal recovery agent, a step of separating the noble metal recovery agent adsorbed with the noble metal from the metal solution, and a separation and a step of recovering the noble metal from the noble metal recovery agent.

The metal solution in which the noble metal is dissolved should just contain the noble metal. The form of the noble metal in the metal solution is not particularly limited, and may be, for example, an ion form or a complex form. Noble metals include, for example, gold, palladium, silver, platinum, rhodium, iridium, ruthenium, osmium, and rhenium.

The metal solution in which noble metals are dissolved may contain metals other than noble metals. Examples of metals other than noble metals include base metals such as copper, iron, zinc, nickel, and tin.

The solution for dissolving the noble metal is not particularly limited as long as it dissolves the noble metal. (iodine solution) can be mentioned.

The acid concentration of the acid solution is not particularly limited, and can be appropriately adjusted according to the type of acid solution, the type and concentration of the noble metal to be recovered, etc., but for example, 0.5 M (mol/L) or more may be, may be 1M or more, may be 2M or more. Also, the acid concentration may be, for example, 13M or less, or 6M or less.

The amount of the noble metal recovery agent to be added when adding the noble metal recovery agent to the metal solution containing the noble metal is not particularly limited. It can be adjusted as appropriate. Specific examples of the amount of the noble metal recovery agent to be added may be, for example, 1 mg or more, or 5 mg or more in terms of dry weight of the active ingredient with respect to 1 mL of a solution having a concentration of 10 μg/mL of the noble metal to be recovered. may be 10 mg or more, may be 15 mg or more, and may be, for example, 100 mg or less, may be 75 mg or less, may be 50 mg or less.

By stirring the metal solution to which the noble metal recovery agent is added for a predetermined period of time, the noble metal can be adsorbed on the noble metal recovery agent. The adsorption time can be appropriately adjusted according to the type and amount of the metal solution and the type and concentration of the noble metal to be recovered. Since the noble metal can be sufficiently adsorbed to the noble metal recovery agent by stirring, for example, the time may be 1 second or longer, 1 minute or longer, 2 minutes or longer, or 3 minutes or longer. Although there is no particular upper limit for the time, it may be, for example, 24 hours or less. The temperature at which adsorption is performed can be appropriately adjusted according to the type and amount of the metal solution and the type and concentration of the precious metal to be recovered. may be 15° C. or higher, and may be, for example, 100° C. or lower, 80° C. or lower, 60° C. or lower, or 40° C. or lower.

The noble metal recovery agent with adsorbed noble metals can be separated from the metal solution by, for example, sedimentation, filtration or the like.

The recovery method according to the present embodiment may further include a refining step of refining the noble metal adsorbed on the noble metal recovery agent after the recovery step. The method for refining the noble metal adsorbed by the noble metal recovery agent is not particularly limited, but for example, a method of burning the recovered noble metal recovery agent to obtain a noble metal as a residue, an acidic thiourea solution, ammonia and an ammonium salt. mixed solution containing, acid solution (e.g., hydrochloric acid solution, aqua regia), alkaline solution (e.g., KOH solution), or metal chelate solution (e.g., EDTA solution) using a predetermined metal elution solution such as precious metals A method of elution and the like can be mentioned.

(Method for recovering precious metals using iodine solution)
An embodiment in which an iodine solution (a solution containing iodine and an iodine salt) is used as the solution for dissolving the noble metal in the method for recovering the noble metal described above will be further described. The recovery method according to this embodiment does not require the use of materials that adversely affect workers and the environment, and can safely recover precious metals. Furthermore, since the necessary materials can be procured at low cost, and the recovery rate of precious metals is high, and the cost associated with mining can be reduced, precious metals can be recovered at low cost. The noble metal to be recovered in the recovery method according to the present embodiment is not particularly limited, but gold or palladium is preferable, and gold is more preferable. The recovery method according to the present embodiment, in which gold is the target of recovery, can be a cheap and safe method that can replace small-scale gold mining using mercury.

The method for recovering precious metals according to the present embodiment includes a step (recovery step) of recovering precious metals from a metal solution in which noble metals, iodine, iodine salts, and reducing agents are dissolved, using the noble metal recovery agent according to the present invention.

In the recovery step, it is important that the metal solution in which the noble metal, iodine, iodine salt, and reducing agent are dissolved is brought into contact with the noble metal recovery agent. Further dissolving the reducing agent in the solution in which the noble metal, iodine and iodine salt are dissolved is considered to produce a metal solution in which the noble metal is dissolved in a form that is easily adsorbed by the noble metal recovery agent. Therefore, the order of addition of the reducing agent and the noble metal recovery agent to the solution in which the noble metal, iodine, and iodine salt are dissolved is arbitrary. Therefore, for example, the noble metal recovery agent may be added to the metal solution in which the reducing agent is further dissolved in the solution in which the noble metal, iodine, and iodine salt are dissolved, or the noble metal, iodine, and iodine salt may be added to the solution. It may be added to the dissolved metal solution together with the reducing agent.

Solvents for the metal solution include, for example, water, lower alcohols (eg, methanol, ethanol, etc.), organic solvents such as acetonitrile, and mixed solvents in which two or more of these are mixed. The solvent is preferably a mixed solvent of water and a lower alcohol, and more preferably a mixed solvent of water and ethanol (aqueous ethanol solution), since it is easy to handle. When using an ethanol aqueous solution, the ethanol concentration in the ethanol aqueous solution may be, for example, 50 to 90 vol%, preferably 60 to 80 vol%.

The iodine salt may be any compound that releases iodide ions in a solvent, and examples thereof include salts of iodine and alkali metals and salts of iodine and alkaline earth metals. Specific examples of iodine salts include lithium iodide, sodium iodide, potassium iodide, magnesium iodide, calcium iodide, barium iodide, rubidium iodide, and cesium iodide. The iodine salts may be used singly or in combination of two or more.

The reducing agent may be an organic reducing agent or an inorganic reducing agent.

Examples of organic reducing agents include ascorbic acid, sodium ascorbate, erythorbic acid (isoascorbic acid), sodium erythorbate, formic acid, oxalic acid, calcium oxalate, sodium oxalate, citric acid and the like. If optical isomers exist in the organic reducing agent, any optical isomer may be used. Examples of inorganic reducing agents include thiocyanide, thiosulfate, sodium sulfide, sulfurous acid, sulfite, and iron powder.

The reducing agent is preferably an organic reducing agent, and ascorbic acid (L-ascorbic acid, D-ascorbic acid and mixtures thereof), sodium ascorbate (L-sodium ascorbate, D-sodium ascorbate and mixtures thereof). more preferred. The reducing agent may be used singly or in combination of two or more.

The content of iodine may be, for example, 0.01 wt % or more and 12 wt % or less based on the total amount of the metal solution. From the viewpoint of further increasing the recovery rate of precious metals, the iodine content is preferably 0.1 wt% or more and 10 wt% or less, and preferably 0.2 wt% or more and 8 wt% or less, based on the total amount of the metal solution. More preferably, it is 0.3 wt % or more and 6 wt % or less.

The content of the iodine salt may be, for example, 0.005 wt % or more and 8 wt % or less based on the total amount of the metal solution. From the viewpoint of further increasing the recovery rate of the noble metal, the content of the iodine salt is preferably 0.05 wt% or more and 6 wt% or less, and 0.1 wt% or more and 5 wt% or less, based on the total amount of the metal solution. is more preferable, and more preferably 0.2 wt % or more and 4 wt % or less.

The content of the reducing agent may be, for example, 0.01 w/v% or more and 8 w/v% or less based on the total amount of the metal solution. From the viewpoint of further increasing the recovery rate of precious metals, the content of the reducing agent is preferably 0.05 w/v% or more and 6 w/v% or less, based on the total amount of the metal solution, and 0.1 w/v% or more. It is more preferably 5 w/v % or less, and even more preferably 0.2 w/v % or more and 4 w/v % or less.

The concentration of the noble metal in the metal solution is not particularly limited as long as the noble metal is dissolved, but is usually 0.00002 w/v% or more and 0.2 w/v% or less based on the total amount of the metal solution. From the viewpoint of further increasing the recovery rate of the noble metal, the concentration of the noble metal in the metal solution is preferably 0.0002 w/v% or more and 0.1 w/v% or less based on the total amount of the metal solution, and 0.001 w /v% or more and 0.05w/v% or less.

The amount of the noble metal recovery agent added may be, for example, 1 mg or more, 5 mg or more, or 10 mg or more in terms of the dry weight of the active ingredient per 1 mL of a solution having a noble metal concentration of 10 μg/mL. , may be 15 mg or more, and may be, for example, 100 mg or less, may be 75 mg or less, may be 50 mg or less.

The method for recovering precious metals according to the present embodiment may further include, after the recovery step, a step (refining step) of refining the noble metals adsorbed on the noble metal recovery agent.

The refining step can be carried out, for example, by burning the noble metal recovery agent to which the noble metal is adsorbed to burn off the noble metal recovery agent, thereby refining the noble metal. Alternatively, for example, a method of refining the noble metal by immersing the noble metal recovery agent to which the noble metal is adsorbed in a metal elution solution to elute the noble metal can be applied. The metal eluting solution includes, for example, an acidic thiourea solution, a mixed solution containing ammonia and an ammonium salt, an acid solution (e.g., hydrochloric acid solution, aqua regia), an alkaline solution (e.g., KOH solution), or a metal chelate solution (e.g., , EDTA solution).

〔kit〕
The invention also relates to kits for recovering precious metals. A kit according to the present embodiment is a kit for recovering a noble metal from a metal solution in which a noble metal, iodine, an iodine salt, and a reducing agent are dissolved, and includes at least a noble metal recovering agent. The kit may further contain a reducing agent in addition to the noble metal recovery agent. The kit according to the present embodiment can be used to dissolve a low-purity precious metal (for example, solid gold such as gold ore) in a solution containing iodine and an iodine salt to recover a higher-purity precious metal. . The kit according to this embodiment can be used to carry out the above-described noble metal recovery method using the iodine solution. The noble metal targeted by the kit according to the present embodiment is not particularly limited, but gold or palladium is preferable, and gold is more preferable.

In the kit according to the present embodiment, the specific aspect of the reducing agent and/or the precious metal recovery agent is the specific aspect of the reducing agent and/or the noble metal recovery agent in the above-described noble metal recovery method and the noble metal recovery method using an iodine solution. can be applied. In addition, when the kit according to the present embodiment contains the reducing agent and the noble metal recovery agent, the reducing agent and the noble metal recovery agent may be included separately in the kit, or may be mixed (for example, the reducing agent and the noble metal recovery agent may be included in the kit) as a mixed powder of

The kit according to the present embodiment may further contain a solution (iodine solution) in which iodine and a salt of iodine are dissolved in the solvent described above, in addition to the reducing agent and the gold recovery agent. As the iodine solution, for example, commercially available tincture of iodine, dilute tincture of iodine, or the like may be used.

EXAMPLES The present invention will be described more specifically below based on examples. However, the present invention is not limited to the following examples.

[Example 1: Preparation of precious metal recovery agent]
Five types of commercially available coffee beans (commercial product 1 to commercial product 5) were prepared. Using commercial products 1 to 5, 10 precious metal recovery agents were prepared as shown below.

As a control, a dry powder of Galdieria sulphuraria, which is known to be capable of selectively recovering precious metals, was prepared (see Patent Document 1). Specifically, G. elegans grown to stationary phase. sulphuraria cells were harvested by centrifugation. The recovered cells were dried at 80° C. for 12 hours, pulverized using a mortar and pestle, and subjected to G.I. A dry powder of sulphuraria was obtained (precious metal recovery agent D).

[Example 2: Noble metal recovery test (1) using noble metal recovery agent]
A recovery test of gold and palladium dissolved in aqua regia was carried out.

(precious metal recovery agent)
Noble metal recovery agent 1-1, noble metal recovery agents 2-1 to 5-2, and noble metal recovery agent D prepared in Example 1 were used.

(Preparation of metal solution)
HAuCl ₄ (final concentration of gold: 100 ppm) and Pd(NO ₃ ) ₂ (final concentration of palladium: 100 ppm) were dissolved in 4M aqua regia to prepare a metal solution. 4M aqua regia was prepared by mixing 36% (w/v) hydrochloric acid and 61% (w/v) nitric acid in a 3:1 molar ratio and diluting 3-fold with distilled water.

(Recovery test)
To 1 mL of metal solution, 20 mg (dry weight) of precious metal recovery agent was added and vortexed. Then, the noble metal recovery agent was precipitated by centrifugation, and the supernatant was recovered.

The gold and palladium concentrations of the metal solution and each supernatant were measured, and the recovery rate (%) was calculated according to the following formula. Gold and palladium concentrations in the metal solution and each supernatant were measured by ICP-OES. In addition, ppm is synonymous with mg/L.
Recovery rate = [{(initial concentration in metal solution) - (concentration in supernatant)}/(initial concentration in metal solution)] x 100 (%)

Table 2 shows the results.

As shown in Table 2, the noble metal recovery agent according to the present invention can recover gold and palladium with high efficiency. In addition, the noble metal recovery agents (precious metal recovery agent 2-2, noble metal recovery agent 3-2, noble metal recovery agent 4-2 and noble metal recovery agent 5-2) containing roasted and ground coffee bean residue as an active ingredient have particularly high efficiency. can recover gold and palladium. Roasted and ground coffee bean residue is a residue after coffee extract is extracted and is usually discarded. According to the present invention, it leads to effective utilization of roasted and ground coffee bean residue (waste), and reduction of environmental load can be achieved.

[Example 3: Noble metal recovery test (2) using noble metal recovery agent]
A precious metal recovery test was conducted in a metal solution containing multiple metal ions (simulated metal waste liquid).

(precious metal recovery agent)
Noble metal recovery agent 1-1, noble metal recovery agent 1-2 and noble metal recovery agent D prepared in Example 1 were used.

(Preparation of metal solution)
A simulated waste solution of gold, copper, palladium, zinc, iron, nickel and tin in 4M aqua regia was used. 4M aqua regia was prepared by mixing 36% (w/v) hydrochloric acid and 61% (w/v) nitric acid in a 3:1 molar ratio and diluting 3-fold with distilled water.

(Recovery test)
To 1 mL of metal solution, 20 mg (dry weight) of precious metal recovery agent was added and vortexed. Then, the noble metal recovery agent was precipitated by centrifugation, and the supernatant was recovered.

(result)
The metal concentration of the metal solution and each supernatant was measured in the same procedure as in Example 2, and the recovery rate (%) was calculated. Table 3 shows the results.

As shown in Table 3, the precious metal recovery agents (precious metal recovery agent 1-1 and noble metal recovery agent 1-2) according to the present invention are obtained by extracting precious metals (gold and Palladium) can be selectively recovered.

[Example 4: Noble metal recovery test (3) using a noble metal recovery agent]
A gold recovery test was performed in a gold solution in which gold was dissolved in an iodine tincture.

(precious metal recovery agent)
Noble metal recovery agent 1-2 prepared in Example 1, noble metal recovery agent D, and G. A precious metal recovery agent L consisting of viable cells of S. sulphuraria was used.

(Preparation of gold solution)
A commercially available iodine tincture (6 wt% iodine, 4 wt% potassium iodide, 60 to 80 vol% ethanol aqueous solution) is added to 70 to 80 vol% ethanol aqueous solution for 1 g of gold ore (including 1.8 to 3.1 μg of gold). (diluted iodine tincture) was added dropwise and stirred for 30 minutes to dissolve the gold. To this solution was added 40 mg of a commercially available vitamin C supplement (food additive grade, 100% vitamin C (L-ascorbic acid)) and 4 mL of water for reduction to obtain a gold solution.

(Recovery test)
To 1 mL of gold solution, 20 mg (dry weight) of precious metal recovery agent was added and incubated for 5 minutes at room temperature with vortexing. Then, the noble metal recovery agent was precipitated by centrifugation, and the supernatant was recovered.

(result)
The gold concentration of the gold solution and each supernatant was measured in the same procedure as in Example 2, and the recovery rate (%) was calculated. Table 4 shows the results.

In Table 4, the dissolution rate (%) indicates the proportion of the gold used dissolved in the dilute iodine tincture. As shown in Table 4, the noble metal recovery agent (noble metal recovery agent 1-2) according to the present invention can recover gold with an extremely high recovery rate (100%). The gold solution used in Example 4 contains gold, iodine, an iodine salt, and a reducing agent. can be recovered. In addition, since coffee bean residue or the like can be used as a precious metal recovery agent, it is possible to reduce the cost and the environmental load. Therefore, the precious metal recovery agent according to the present invention is also useful as an alternative to small scale mining.

[Example 5: Noble metal recovery test (4) using noble metal recovery agent]
(precious metal recovery agent)
A silver bark obtained from a coffee bean manufacturer was pulverized using a mortar and pestle to obtain a precious metal recovery agent (pulverized silver bark).

(Preparation of gold solution)
10 mL of commercially available iodine tincture (6 wt% iodine, 4 wt% potassium iodide, 60-80 vol% ethanol aqueous solution) diluted twice with 70-80 vol% ethanol aqueous solution (diluted iodine tincture) was added dropwise to 2 mg of gold powder. , and stirred for 30 minutes to dissolve the gold. 40 mg of commercially available vitamin C supplement (food additive grade, 100% vitamin C (L-ascorbic acid)) and 4 mL of water were added to 1 mL of this solution for reduction to obtain a gold solution.

(Recovery test)
To 1 mL of gold solution, 20 mg of precious metal recovery agent (pulverized silver skin) was added and incubated for 5 minutes at room temperature while stirring with a vortex. Then, the noble metal recovery agent was precipitated by centrifugation, and the supernatant was recovered.

(result)
The gold concentration of the gold solution and each supernatant was measured in the same procedure as in Example 2, and the recovery rate (%) was calculated. As a result, the recovery rate was 90.3%. The precious metal recovery agent (pulverized silver coating) according to the present invention can recover gold at a high recovery rate. As in Example 4, the gold solution used in Example 5 was a solution of gold, iodine, iodine salts, and a reducing agent, and did not use materials that adversely affected the workers involved in gold recovery and the environment. Since there is no gold, it is possible to recover the gold safely. In addition, the silver skin is obtained in large quantities during the production of coffee beans, and is currently discarded because there is no way to use it. According to the present invention, since this silver skin can be used as a precious metal recovery agent, it is possible to reduce the cost and environmental load. Therefore, the precious metal recovery agent according to the present invention is also useful as an alternative to small scale mining.

Claims (6)

A step of recovering gold from a metal solution in which gold is dissolved with a gold recovery agent,
A method for recovering gold, wherein the gold recovery agent contains coffee cherries as an active ingredient . The recovery method according to claim 1, wherein the active ingredient is coffee beans or silver bark. 3. The recovery method according to claim 2, wherein the coffee beans are at least one selected from the group consisting of ground husks, roasted coffee beans, roasted and ground coffee beans, and roasted and ground coffee bean residues. The recovery method according to any one of claims 1 to 3 , wherein the metal solution is a solution in which gold, iodine, an iodine salt, and a reducing agent are dissolved. The recovery method according to claim 4 , wherein the salt of iodine is at least one selected from salts of iodine and alkali metals and salts of iodine and alkaline earth metals. The recovery method according to claim 4 or 5 , wherein the reducing agent contains ascorbic acid.